It is known in the art that electromagnetically cast ingots exhibit surface perterbations that are detrimental during subsequent processing and which are also detrimental in recovery achieved thereby. These surface defects most often take the form of longitudinal pleats or standing waves that set up within the contained molten metal during the electromagnetic casting process. Such defects are particularly relevant in the region adjacent to the electrical connections of the inductor. Discussions of such surface defects can be found in Canadian Pat. No. 930,925 to Getselev, and U.S. Pat. No. 3,702,155 to Getselev.
It is also known from the prior art that electromagnetically cast rectangular ingots are often cast with high radius of curvature ends which is indicative of the need for improved shape control at the corners of such ingots. Reference is made to our copending U.S. application, Ser. No. 1,730, filed January 8, 1979 and entitled "Ingot Shape Control By Dynamic Head in Electromagnetic Casting", which disclosure is hereby incorporated by reference.
In U.S. Pat. No. 3,605,865 to Getselev a non-magnetic screen is utilized to properly shape the magnetic field for containing the molten metal being electromagnetically cast. In addition to screen utilization, solution of the problem of ingot shape may be sought through electromagnetic field modification, utilizing shaped inductors (U.S. Pat. 4,004,631 to Goodrich et al.) or by utilizing both screens and shaped inductors (U.S. Pat. No. 3,985,179 to Goodrich et al.).
Other means of enhancing and controlling ingot shape is by utilization of a hot-top or open-ended container placed before and adjacent to the electromagnetic casting station, as depicted in copending U.S. Ser. No. 876,912 filed Feb. 13, 1978 and entitled "Improved Process for Electromagnetic Casting of Copper and Copper Base Alloys", which is a continuation in part of U.S. Ser. No. 752,458 filed Dec. 20, 1976, now abandoned.
A general discussion of the use of conductor pairs and grids to provide electromagnetic forces useful in the shape control of metal castings appears in the article "Electromagnetic Ingots Molds. I. Theoretical Treatment", Z. Metallk (1977) by Hermann Jehn, Eckehard Fromm and Preter Neuschutz, pp. 397-409.